RFID technology has become well-known over the past few decades, and its wireless potentialities continue to be expanded and exploited. Implementing an RFID device has certain basic features. The simplest RFID device is the TAG. The tag is typically a completely passive device in that it contains no internal power source; a passive tag derives its operating power from the RF field used to interrogate the tag. A passive RFID Tag 100 is shown as a block diagram in FIG. 1. However, it should be noted that tags can be active also.
The tag's only link to the outside world is normally the antenna 110, shown in FIG. 1 with connections LA and LB. When the antenna picks up an RF field of the proper amplitude and frequency, an operating voltage is generated that can power 120 the tag. The demodulator 130 extracts commands and data from the RF field and passes them along. The digital control block 140 interprets the received commands and data and formats responses. Tag responses are encoded and transmitted by the modulator 150. The memory block 160 stores received data and supplies data for responses. Since the operating voltage comes from the RF field, the contents of a volatile memory are lost when the field is not present. Non-volatile memory contents are maintained even in the absence of an RF field.
This tag architecture is described herein as a passive RFID device, wherein the entire data module is completely passive. As mentioned, the tag's only link to the outside world is normally the antenna, which is true for commercially available tags.
An active device is used in order to read from or write to a passive tag. This active device is commonly known as a reader/writer. The reader/writer generates the RF field that powers the tag. The reader/writer formats and transmits commands to the tag and receives responses back from the tag. FIG. 2 shows the block diagram of a reader/writer 200.
A higher-level device such as a computer or embedded micro-controller (the host system 210) controls operation of the reader/writer, which utilizes an RF board. In effect, the reader/writer is a kind of modem or transceiver that interfaces between the host system 210 and the RFID tag. Typically the reader/writer does no processing of the data passing between the RFID tag and the host system; it merely passes data between the two. With these two devices (i.e. the tag and reader/writer), systems can be built. The simplest Radio frequency identification (RFID) systems typically use one or more reader antennae of a reader/writer to send radio frequency (RF) signals to items tagged with RFID tags. The use of such RFID tags to identify an item is well known in the art. In response to the RF signals from the reader (which may also have writer capability), the RFID tags, when excited, produce a disturbance in the magnetic field (or electric field) that is detected by the reader antenna. Throughout this application, the term “reader” may also include a writer, and conversely, the term “reader/writer” may only include a reader. As mentioned, RFID tags are passive tags that are excited or resonate in response to the RF signal from the reader antenna when the tags are within the detection range of the reader antenna.
A system using multiple antennae powered by a single reader unit and using a multiplexer switch to alternate between the antennae is also known in the art. Such a system 300 is conceptually represented in FIG. 3, where separate antennae 301 to 305 are connected to a reader 309 and multiplexer unit 310 through respective transmission cables, via solder points 311 to 317 and 321 to 325. The use of multiple antennae typically improves the spatial coverage when reading tags, without requiring more than one reader unit.
As shown in FIG. 4, such a system 400 is often used to identify and locate tagged items 401 and 402 on a shelf or on multiple shelves 411 to 416 in a cabinet. FIG. 4 shows fixed antennas 421 to 426 located at various locations in the shelving system, and these antennas may have separate RFID readers, but preferably the antennas can be linked to a shared RFID reader 430 as shown in FIG. 4. Of course, the antennas 421 to 426 are shown to explain the concept, and are not precise examples of a real system.
The main disadvantage of the arrangement disclosed in FIG. 3 and FIG. 4 is that the reader antennae are fixed in place and are not easily replaceable or reconfigurable. The user cannot modify the RFID antennae configuration to account for changing product sizes and/or product tag location. This type of functionality forces the production of multiple design configurations that is both expensive and time-consuming, and may not even be useful to the end user.
Another shortcoming of the prior art design is in the difficulty of replacing a damaged antenna. A skilled technician would be responsible for disassembly and replacement of the unit, which will be time-consuming and costly.